1. Field of the Invention
This invention is generally concerned with the use of freezing conditions in order to accomplish a degree of separation of a solvent or solute from a solute/solvent liquid solution. It is particularly concerned with the use of gas evolution to produce such freezing conditions. The herein disclosed processes have many useful ecological and industrial purposes, but they are especially well suited for: (1) converting seawater, brackish water, etc., into potable water, (2) recovering metals such as magnesium from seawater or other salt-containing bodies of water, (3) demineralizing "fresh" waters used to make carbonated beverages, (4) recovering solutes and/or solvents from industrial solute/solvent solutions and (5) cleaning up polluted bodies of water such as lakes, rivers, streams, groundwaters, etc.
Numerous methods have been suggested and/or developed for employing freezing conditions to produce potable water or other "pure" solvents or solutes from solute/solvent solutions. Most of these processes have not, however, experienced wholehearted acceptance. For example, one of the principal problems inherent in most desalination processes that employ freezing conditions as their modus operandi is their inability to produce potable water at economically acceptable costs. Not only must these processes be able to produce large volumes of potable water, they also must be able to do so at locally acceptable costs. Cost considerations are particularly important because many areas of the world having the most acute potable water shortages also are characterized by their very low income levels.
In many processes employing freezing conditions to produce potable water, the subject water is simply frozen to produce an ice product that is then melted to obtain "pure" water. Flash-freezing is also employed to produce water vapor products that are recondensed to obtain pure water. Both of these freezing techniques require a great deal of expensive refrigeration and/or compressor capacity. Flashfreezing techniques are especially expensive because they employ vacuum/freezer apparatus wherein a vacuum must be created to evaporate the entire volume of the water thus produced. Such evaporation can only be accomplished by the expenditure of a great deal of mechanical work. The water vapor thus created then must be condensed back to its liquid form by another large expenditure of mechanical work. The refrigeration, vacuum creation and condensation steps of such processes require considerable amounts of mechanical and/or electrical energy that can only be obtained at high fuel and capital costs. Consequently, freezing and flash-freezing processes have not been widely employed to produce potable water. Another approach to lowering the expenses associated with freezing a solute/solvent solution involves dissolving a gas such as carbon dioxide into such a solute/solvent solution. Then, after the temperature and pressure of the solution is adjusted, a Joule-Thompson free expansion of the resulting solute/solvent solution is forced by spraying it through a nozzle. In effect, this spraying produces a three phase separation of the solute/solvent solution.
2. Description of the Prior Art
U.S. Pat. Nos. 5,084,187 ("the 187 patent") and 5,167,838 ("the 838 patent") to Wilensky (hereinafter the "Wilensky patents") represent the closest art to the processes described in this patent disclosure. Indeed, many of the teachings of the Wilensky patents help to clarify the teachings of the present patent application, and hence, these patents are incorporated herein by reference. Generally speaking, the Wilensky patents teach that a solute can be separated from a solute/solvent solution by: (a) dissolving a gas such as carbon dioxide into the solution to produce a single-phase composite liquid, (b) raising the pressure on the liquid, (c) lowering the temperature of the liquid and (d) performing a Joule-Thompson free expansion on the entire mass of composite liquid by spraying it through a nozzle under pressure supplied by a pump.
Applicants have postulated that Wilensky's method of performing his Joule-Thompson free expansion--forcing the entire liquid mass through a nozzle--may not achieve maximum ice production for a given expenditure of mechanical energy. Applicants do not wish to be strictly bound to such a theory, but they have reason to believe that a lower than theoretically possible amount of ice production by the Wilensky processes may follow from the fact that the carbon dioxide vapors produced by a Joule-Thompson free expansion of an entire liquid mass through a nozzle may not provide sufficient time to fully associate the emerging carbon dioxide vapors with the liquid-phase material (e.g., brine). This lack of association time between the carbon dioxide vapor and liquid-phase material (e.g., water) tends to limit production of a small (but very important) amount of solvent vapor (e.g., water vapor) from the liquid phase material (e.g., water) when pressure is suddenly released from the liquid just after it clears the nozzle employed in the Wilensky processes. Applicants believe that the carbon dioxide/liquid exposure time is particularly important because of its effect on the amount of solvent vapor that can be created by such a process. This, in turn, is important because the water vapor provides most of the refrigeration created these vaporization processes. In other words, applicants have determined that greater amounts of ice can be formed as more solvent (e.g., water) vapor is produced. Consequently, applicants' processes are designed to produce more water vapor than can be created from the Wilensky processes with comparable energy expenditures. Moreover, the herein described processes, at the very least, save the mechanical energy needed by the Wilensky processes to pump an entire mass of liquid through a nozzle constriction to achieve a Joule-Thompson free expansion of the entire mass of that liquid.